The present invention relates to an apparatus for driving a medical appliance such as an artificial heart or balloon pump in the main artery, and more particularly to a fluid driving apparatus for regularly changing a fluid pressure in accordance with the instructed parameter.
From the standpoint of safety, it is important for an artificial heart to be driven to give blood with a pulsatory current which is closely analogous to pulsation of a heart in the living body. There are known various artificial hearts of diaphragm type, sack type, piston type, etc., which are generally driven by receiving the predetermined pressure from a fluid such as air. In order to drive the artificial heart under the optimum conditions best suitable for the state of the living body, a driving apparatus is required which can output a precise pressure in accordance with those conditions at the given timing. In other words, the driving apparatus is preferably capable of setting all parameters such as heart rate, positive (plus) pressure, negative (minus) pressure, duration or duty ratio for applying the positive and negative pressure to the artificial heart, etc. to the respective predetermined values precisely and promptly.
In the conventional driving apparatus for an artificial heart, mechanical pressure reducing valves or the like are employed in the positive and negative pressure systems separately to serve as means for obtaining the desired precise pressures. However, in the usual driving apparatus for an artificial heart an output terminal of the positive pressure system is interconnected with an output terminal of the negative pressure system, so that the negative pressure becomes a load of the positive pressure system and the positive pressure becomes a load of the negative pressure system. This results in such a disadvantage that, upon adjusting the negative pressure, for example, the load of the positive pressure system is changed correspondingly and hence the positive pressure is also changed, and upon adjusting the positive pressure, the load of the negative pressure system is changed correspondingly and hence the negative pressure is also changed. In the past, therefore, even when adjusting one pressure, it must be carefully adjusted such that two pressure reduction regulating valves are simultaneously operated while confirming two pressure readings, and one pressure is updated while keeping the other pressure at a predetermined value. This leads to a defect in that pressure adjustment requires a great deal of skill and is time consuming.
In view of the above, the applicant of this patent application has previously proposed an artificial heart driving apparatus (U.S. patent application Ser. No. 480,181) in which solenoid valves for regulating pressures are provided in the positive and negative pressure systems, respectively, thereby achieving highly accurate pressure adjustment and facilitating setting of various parameters
In the artificial heart driving apparatus of this type, since the positive and negative pressures are alternately applied to the artificial heart, a fluid must be alternately applied and discharged, whereby a large amount of driving fluid is consumed. Accordingly, air is generally used as a driving fluid.
In an artificial heart driven with a fluid, however, the driving fluid is separated from blood by just a thin film. Thus, if the artificial heart should fail, the driving fluid may leak through the thin film. In such an event, if air is used as a driving fluid, blood is coagulated and this endangers the patient's life.